The present invention relates to a key guide structure for use in a keyboard apparatus, having keys pivotably mounted on a key frame, which guides pivoting movement of a key by means of a key-side guide member provided on an inner wall surface of the key and a frame-side guide member provided integrally with the key frame.
Key guide structures of the aforementioned type are disclosed, for example, in Japanese Patent Laid-open Publication No. HEI-9-244656 (patent literature 1) (corresponding to U.S. Pat. No. 5,824,928) and Japanese Patent Publication No. 3044810 (patent literature 2). In the key guide structure disclosed in patent literature 1, a key guide is disposed on an upper portion of a front plate of a frame and inside a distal end portion of a white key, and movement of the white key is guided by cooperation between the key guide and two side surfaces (side walls) of the while key which are opposed to each other in a direction in which a plurality of white keys are arranged (hereinafter “key-arranged direction”).
In the key guide structure disclosed in patent literature 2, a key guide is provided vertically on a front portion of a keyboard frame, and a guided section is accommodated within a lower stopper provided on a front end portion of a key. The key is guided by cooperation between the key guide and two side surfaces of the key which are opposed to each other in a key-arranged direction. Patent literature 2 also discloses that a slight amount of grease is put between the key guide and the guided portion.
According to the disclosure of patent literature 1 and patent literature 2, the key guide structure is constructed to guide a key by the key guide contacting, for example, the key's inner side surfaces opposed to each other in the key-arranged direction (i.e., in a width direction of the keyboard). Thus, the disclosed key guide structures would present various problems pertaining to dimensional stability, positional accuracy and appearance of the keys, etc.
Typical example of the size stability problem is as follows. In general, keys are each formed by molding into a downward-opening box-like shape. Thus, due to change (e.g., temporal change) and variation (difference) in resin molding conditions and aftercontraction (or deformation after molding) of the resin molds, the greater the height of the opposed side surfaces of the keys, the more instable would become the dimensions of the opposed side surfaces. Further, regions of the opposed side surfaces farther from the front or rear end surface (i.e., closer to the lengthwise middle) of the keys tend to become instable in dimension (or distance) between the side surfaces. Thus, keys can not be molded accurately into originally-designed dimensions. Thus, unintended contact would occur between the key and the corresponding key guide, with the result that there would arise problems with the key guide function, such as unsmooth vertical movement of the key, noise sound produced due to the unsmooth contact between the key and the key guide, etc.
Typical example of the key position problem is as follows. Each key is positioned in a left-right horizontal direction by the corresponding key guide positioned between the pivot point and distal end of the key. Thus, the closer to the pivot point of the key (i.e., the farther from the distal end) the position of the key guide (key guide section), the more difficult would it become to achieve positional accuracy, in the key-arranged direction, of the key's distal end portion, which would result in great differences in gaps between adjoining keys.
Typical example of the key appearance problem is as follows. In a case where the key guide is located at a position Pa or Pb as shown in FIG. 9, it has been known to provide a rib Ra or Rb near the key guide Pa or Pb to interconnect the opposed side surfaces and thereby prevent deformation (inward warpage) of the side surfaces. However, unwanted sinkage or sink tends to occur in the outer surface of a portion where the rib Ra or Rb is provided. Further, the greater the distance between the side surface of the key (i.e., width of the key), or the greater the height of the rib, the more easily such sink tend to occur. Therefore, the key position problem can be avoided more easily if the position Pa of the key guide section of FIG. 9 is closer to the distal end (front end surface) of the key; in such a case, however, the outer surface of the portion where the deformation-preventing rib Ra is provided may sink more easily than where the key guide section is at the position Pb, and thus, the appearance of the outer surface would be aesthetically impaired. Further, if base portions of the rib are reduced in thickness with a view to avoiding the unwanted sink, it is necessary to provide a slide mechanism (i.e., core sliding toward the rear of the key) in a molding mold, and thus, a space extending toward the rear of the key is required for sliding movement of the slide mechanism.